One known type of field marker includes a disc on the end of a long arm that, in use, extends from the side of the implement with which the marker is being used. To store such an arm for transport, folding or knee-action arms have been developed. With air seeders, these markers are designed to be mounted on the front corner of the cultivator frame in order to avoid interference with the tank of the seeder and to prevent projection of the marker past the rear of the seeder. Air seeders are very sensitive to weight distribution. Mounting a marker on the front corner of the seeder frame causes tilting of the frame and uneven seeding depth.
Another problem with known markers is creep of the marker arm from its correct marking position when in use. There is considerable drag on a marker and this is resisted by the hydraulic cylinder that pushes the marker out to its in use position and maintains it in that position. While a locking valve may be used to hold the cylinder in the extended condition, leakage past the piston will occur, causing the marker to creep rearwardly out of position.
The folding or knee-action markers are relatively complex structures. To unfold the arm, mechanical arms, cables or chains and associated components are used.
The present invention is concerned with certain improvements in disc type field markers that are intended to ameliorate the problems of the prior art.